How Shale Helped Frack Mexico's Energy Impasse

After decades of inertia, the energy-reform proposal given general approval by the Mexican Senate late Tuesday goes even further than many had expected. The country's rapidly changing energy relationship with its northern neighbor helps explain why.

Mexico's dismal decline in oil production, to 2.94 million barrels per day last year from 3.85 million in 2004, is the obvious impetus for trying to coax in more foreign money and...